Een nieuwe erwtenmossel voor Nederland: de Samengedrukte erwtenmossel Euglesa compressa (Prime, 1852)

Recently the pea clam Euglesa compressa (Prime, 1852) (syn. Pisidium compressum) was discovered as new to France. However, historical data revealed the occurrence of morphologically similar pea clams collected in 1940, 1961, 1977 and 1982 in northeast Germany, referred to as Pisidium casertanum forma plicatum Zeissler, 1971. The first find of this ‘forma’ in the Netherlands was in 1990 (empty valves); since about 1995 it is considered common in the Dutch Rhine-Meuse delta. This Pisidium casertanum forma plicatum proved to be identical to the North American species Euglesa compressa. This paper focuses on the distinction between Euglesa compressa and the morphologically similar Euglesa supina (syn. Pisidium supinum A. Schmidt, 1850).